dabaobao wrote:
If n and k are integers, is (−1)^(4n+k) less than 0?
(1) n is an even number
(2) k is an odd number
C-Trap Q
Theory:
(-1)^even power = always +
(-1)^odd power = always -
Simplify the Q
4n is always even. So (-1)^4n would always be +
So we only care about (-1)^k. If we know the power of k, then we can tell whether (−1)^(4n+k) is <0 or >0.
Hence, simplified Q: Is k even or odd?
Solving the Simplified Q
1) Don't care about whether n is even or odd since 4n would always be even. Hence (−1)^(4n) would be even. Need k. Not sufficient.
2) K=odd. This is what we wanted sufficient.
Make sure to not fall in the C-Trap by thinking that you need both k and n. This is a common trap that GMAT likes to use on 700 level Qs.
Hence, answer = B.
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